In recent years, the development of information communication technologies promoted transmission and reception of data of documents, pictures, etc. through networks such as the Internet. Particularly, in the case of communication terminals such as cell phones, where a user switches a model to another or where a user selectively uses a plurality of communication terminals, data such as information about the user, a telephone directory, etc. is transferred to another communication terminal, for example, upon replacement of UIM (User Identity Module). During the transfer of data, conversion (encryption) of the data according to a predetermined rule is an effective means for preventing unauthorized access to the data or falsification of the data by a third party in the middle of communication.